Arboreality is a central component in theories regarding the origin and subsequent radiation of the Primate Order, and most extant primate species do spend the majority of their time in the trees. However, a few living species of primates are primarily terrestrial, and fossil evidence suggests that terrestriality may have been more common in the past, possibly evolving independently in several lineages. Indeed, it has been suggested that some of the earliest monkeys and apes, not to mention the ancestors of our own species, were at least partly terrestrial. However, while many studies have identified behavioral and morphological specializations of primates associated with arboreal habits, relatively little is known about the functional morphology of features related to terrestriality. Digitigrade hand posture during quadrupedal locomotion, although considered a hallmark of terrestrial habits, is one such feature about which little is known. The goal of the present study, therefore, is to examine the biomechanics of different hand postures in primates by drawing upon biomechanical theory proposed for different postures observed in the distal extremities in other mammals. Specifically, this study will quantify the locomotor mechanics associated with digitigrade versus palmigrade hand postures in two closely related Old World monkey species during quadrupedal locomotion. Two lines of investigation will be presented: 1) experimental analysis of primate quadrupedal locomotion on both terrestrial and simulated arboreal substrates to quantitatively describe and compare different hand postures; and 2) an exploration of the association between the kinematics and kinetics of different hand postures on metacarpal bone strain using computer simulated finite element analysis (FEA). This analysis will provide a better understanding of the adaptive value of digitigrade hand postures in a functional context, and these results can in turn be applied to derive anatomical measures to be better able to interpret fossil material. Thus the results of this analysis will improve our knowledge of form:function relationships, and aid in the understanding of the course of primate locomotor evolution, including that of our own species. In addition, resolution of the biomechanics of digitigrady in primates may offer new insight into why digitigrady has evolved numerous times in vertebrates.
The broader impacts of this work stem from the integration of research in multiple scientific disciplines including anthropology, functional morphology, and bioengineering. The Co-PI will be sufficiently trained using sophisticated techniques including three-dimensional motion and force plate analysis, bone strain, and finite element analysis to address a variety of questions related to animal locomotion in the future as an independent researcher. Undergraduate and other graduate students at Stony Brook University will be encouraged to participate in this research to learn experimental techniques as well as to explore their own research questions with the animal subjects acquired with this proposal. All finite element models will be made publicly available to promote collaborative research and to provide the opportunity for independent tests of the models. This research is expected to be of interest to a wide scientific community including researchers in anthropology, paleontology, biomechanics, bone biology, biomedical engineering, veterinary science, and sports medicine.
